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CNIT 121: 13 Investigating Mac OS X Systems

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Slides for a college course based on "Incident Response & Computer Forensics, Third Edition" by by Jason Luttgens, Matthew Pepe, and Kevin Mandia.

Teacher: Sam Bowne
Twitter: @sambowne
Website: https://samsclass.info/121/121_F16.shtml

Published in: Education

CNIT 121: 13 Investigating Mac OS X Systems

  1. 1. CNIT 121: Computer Forensics 13 Investigating Mac OS X Systems
  2. 2. Topics
  3. 3. HFS+ and File System Analysis • Hierarchical File System features:
  4. 4. Nine Structures 1. Boot blocks 2. Volume header 3. Allocation file 4. Extents overflow file 5. Catalog file 6. Attributes file 7. Startup file 8. Alternate volume header 9. Reserved blocks
  5. 5. Nine Structures 1. Boot blocks • First 1024 bytes of volume • Typically empty on modern systems 2. Volume Header and Alternate Volume Header •Located 1024 bytes from the beginning of the volume •Information about the volume, including the location of other structures
  6. 6. iBored Disk Editor for Mac
  7. 7. Mac Timestamps •All in local time •HFS+ Volume •Create date, modify date, backup date, checked date •File •Access, modify, inode change, inode birth time (file creation)
  8. 8. Stat Command • Shows all four timestamps on Mac
  9. 9. Allocation File • A bit for every block • 1 = in use • 0 = available
  10. 10. Extents Overflow File • "Extents" are contiguous allocation blocks
  11. 11. Catalog File • Details hierarchy of files and folders in the system • Each file and folder has a unique catalog node ID (CNID)
  12. 12. Attributes File • Optional • Used for named forks • Additional metadata assigned to a file • Like Microsoft's Alternate Data Streams • Stores origin of files from the Internet, and tags like "Green" and "Important"
  13. 13. Startup File • Not used by Mac OS X • Usually empty
  14. 14. File System Services • Spotlight • Managed Storage
  15. 15. Spotlight • Metadata indexing and searching service • Indexers examine the content of files to find keywords • Some index entire content, others only import metadata
  16. 16. Spotlight • Can be used to search a live system • Not much use for a static acquisition • Indexes are deleted when a file is deleted • No tools are available to parse the data stored by the Spotlight indexer once it's extracted from a drive image
  17. 17. Managed Storage • New in Mac OS X Lion (10.7) • Allows apps to continuously save data • Uses daemon "revisiond" • Saves data on volumes under the "hidden" directory • /.DocumentRevisions-V100
  18. 18. Capturing db Files • Copy them to another folder • Originals are in use and won't open • db.sqlite shows files used with timestamps
  19. 19. • Consider the file with file_storage_id 6
  20. 20. Generations • 394 versions of that file saved • With timestamps and other info.
  21. 21. Core Operating System Data
  22. 22. File System Layout • Four domains for data classification • Local • System • Network • User
  23. 23. Local Domain • Applications and configurations that are shared among all users of a system • Administrative privileges required to modify data in this domain • These directories are in the local domain:
  24. 24. System Domain • Data installed by Apple, and a few specialized low-level utilities • Most useful domain for intrusion investigations because it contains the system logs • Includes all the traditional Unix structures, all of which require administrative privileges to modify • /bin, /usr, /dev, /etc, and so on, also /System
  25. 25. Network Domain • Applications and data stored here is shared among a network of systems and users • In practice, rarely populated with data • Located under the /Network directory
  26. 26. User Domain • Primary source of data for most other investigations • Contains user home directories and a shared directory • All user-created content and configurations will be found under /Users • High-privilege and Unix-savvy users may break this model
  27. 27. MacPorts Package Manager • Lets you add BSD packages to your Mac • Very useful • Requires command-line developer tools • Link Ch 13b
  28. 28. The Local Domain
  29. 29. /Applications • Nearly every installed application is here • Application Bundles • Contain everything an application needs to run: • Executable code, graphics, configuration files, libraries, helper applications and scripts
  30. 30. Application Bundles • Finder treats the bundle as a single file • Most common extensions
  31. 31. Inside the Bundle • Right-click, Show Package Contents • Subdirectories • MacOS, Resources, Library, Frameworks, PlugIns, SharedSupport • Developers can put anything in these directories • VMware Fusion's Library folder contains command- line utilities to manage the VMware hypervisor
  32. 32. Console App
  33. 33. Package Contents • Contains additional metadata • Time and date stamps show when the app was installed • A good place to hide data
  34. 34. /Developer • Used by XCode, Apple's development environment • Until recently, all development tools, SDKs, documentation, and debugging tools were here • Later versions of XCode moved the tools • This directory may still be present on some systems
  35. 35. /Library • /System/Library • App settings for the operating system • /Library • Settings shared between users • /Users/username/Library • User-specific settings
  36. 36. Application Support • /Library/Application Support • /User/username/Library/Application Support • Settings, caches, license information, and anything else desired by the developer
  37. 37. Caches • /Library/Caches • /User/username/Library/Caches • Temporary data for applications
  38. 38. Frameworks • /Library/Frameworks • /System/Library/Frameworks • Drivers or helper applications, for applications • Usually nothing significant here
  39. 39. Keychains • /Library/Keychains • /System/Library/Keychains • /User/username/Library/Keychains • Passwords and certificates • Requires user's password to open
  40. 40. Logs • /Library/Logs • /User/username/Library/Logs • Application logs • Very important to review
  41. 41. Preferences • /Library/Preferences • /User/username/Library/Preferences • Application preferences, if the application allows a system API to manage them • Stored in .plist files • Comparable to the Software hive in Windows
  42. 42. Receipts • /Library/Receipts • /User/username/Library/Receipts • Files here are updated when an application is added to the system • InstallHistory.plist contains information about every application installed via the OS's installer or update framework
  43. 43. WebServer • /Library/WebServer • Apache, installed on every copy of Mac OS X, is started when a user turns on Web sharing • This folder is Apache's Document Root
  44. 44. File Types • Used by nearly every application • Property lists (.plist) • Tools: plutil on Mac, "plist Explorer" on Windows • SQLite databases • Tools: Firefox Plugin SQLite Manager, sqlitebrowser
  45. 45. The System Domain
  46. 46. Traditional Unix Paths • Some investigations are based entirely on data found here, such as log files • /System directory is structured similarly to the 
 /Library directory • Locations where applications maintain persistence • Requires administrator privileges to create or modify files
  47. 47. Artifacts • System logs in /var/log • Databases in /var/db • Records of printed data in the CUPS log • System sleep image • Software imported using MacPorts or Fink, or compiled in place, may be in /opt
  48. 48. The User Domain
  49. 49. User-Created Content
  50. 50. Specific Sources of Evidence
  51. 51. User and Service Configuration • Apple uses LDAP for enterprise management and Directory Services for local user management • Directory Services doesn't use the traditional Unix files /etc/passwd and /etc/groups • Data in SQLite databases and binary-formatted property lists
  52. 52. The Evidence • Directory Service data is in 
 /private/var/db/dslocal • Databases (or nodes) for the local system are in the subdirectory nodes/Default • My password hash is on the next slide • More info at links Ch 13c and 13d
  53. 53. Password Hash
  54. 54. Decoding the Password Hash
  55. 55. Other Configuration Options
  56. 56. sqlindex • In /private/var/db/dslocal • Maintains creation and modification time for the plist files in the directory structure • And information on the relationships between the data • Automatically backed up to /private/var/db/ dslocal-backup.xar (a gzip tar file)
  57. 57. Analysis of sqlindex • Shows when a share was created • Whether an account existed,and its privilege level
  58. 58. User Accounts
  59. 59. Sharepoints • Status of the share for • AFP (Apple Filing Protocol) • SMB (Server Message Block) • FTP (File Transfer Protocol) • Sharepoint names and share path • When the share was created
  60. 60. Trash and Deleted Files • Files deleted from USB sticks go into a Trash folder on the stick, labeled by user ID, like • /Volumes/USBDRIVE/.Trashes/501
  61. 61. System Auditing, Databases, and Logging • Open Source Basic Security Module (OpenBSM) • Powerful auditing system • Logs: • File access • Network connections • Execution of applications and their command- line options
  62. 62. OpenBSM • Default configuration doesn't save detailed information and is of limited use for IR • Configuration files in /etc/security • Primary file is audit_control
  63. 63. OpenBSM • This configuration will log everything for all users, and • Login/logout, administrative events, processes, and network activity
  64. 64. Helper Services • Run in background • Track events or common data • Maintain state with SQLite databases or property list • Examples:
  65. 65. Airportd • Runs in an application sandbox • Configured in /usr/share/sandbox
  66. 66. Airportd Plist
  67. 67. Networks
  68. 68. System and Application Logging • Many log and forensic artifacts in these folders • Most are in plaintext, some are binary
  69. 69. Read with Syslog
  70. 70. Other ASL Log Files • Filenames starting with BB • Authentication logs from long ago • Year is 1 year after the correct date
  71. 71. Other ASL Log Files • Filenames starting with AUX • Backtrace for crashed or abnormally terminated applications • Plaintext
  72. 72. /private/var/audit • Read with praudit
  73. 73. Example Log Entries • Erase flash drive • Failed login attempt
  74. 74. Interesting Items in Log • iCloud connection, Time Machine, iTunes • Indicates that there are backups of data on other devices
  75. 75. Scheduled Tasks and Services • Apple moved from cron to launchd • Commands to execute at startup
  76. 76. Properties for LaunchAgents
  77. 77. Application Installers • When an application is installed, two files are placed in /private/var/db/receipts • Bill of Materials (BOM) and plist
  78. 78. • BOM contains a complete inventory of files • Plist contains install date, package identifier, and path access control lists Application Installers

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